The invention relates to a process for taking a representative milk sample and to an apparatus, particularly for performing the process.
A process and an apparatus of the aforementioned type are e.g. known from DE 35 02 858 A1. In the known apparatus a milk sample is actively pumped by means of a peristaltic pump from a delivery line into a sample bottle for example during the transfer of a milk charge from one container to another. The peristaltic pump is controlled in such a way that, in accordance with a previously inputted desired quantity for the milk charge, the sample bottle for the latter is filled in accordance with a desired volume.
In order to obtain a reproducible desired volume, it is necessary to have information on the acceptance capacity of the milk collecting container which may be a truck or trucks. For this purpose hitherto one parameter has been fixedly predetermined in a preprogrammed manner, so that the sample bottle for receiving the milk sample has been constantly filled to a greater or lesser extent.
As the aim is to take a continuous representative milk sample of the entire milk charge, the milk sample removal process must be controllable as a function of the total milk charge volume. The term a representative milk sample is understood to mean that only a maximum volume is available in the sample bottle intended for the milk sample and on the other hand that, if possible, the milk sample should have a roughly constant volume, independently of whether a lower volume milk charge or a very large milk charge is delivered. The sought constant volume for the milk sample results from the fact that certain minimum milk sample quantities are required for investigations and tests.
Another objective of the representative milk sample is to draw the latter over the entire delivery cycle of the corresponding milk charge. However, since, as a function of the volume, the milk charges are sucked with different deliveries, e.g. from a tank and pumped into the milk collecting truck or tanker, so that different delivery times occur, account must also be taken of this aspect within the scope of a representative milk sample.
In addition, when using a peristaltic pump for taking a representative milk sample, a further problem occurs in that the delivered volume is not in a linear relationship with the speed of revolution of the peristaltic pump. If it is assumed, for example, that a peristaltic pump delivers a volume z1 after y revolutions in the case of a speed of revolution of x1, then normally the volume z2 delivered at a higher speed x2 after y revolutions will be smaller than z1. This is attributed to the fact that the hose or tube used does not have sufficient time, particularly if high speeds are used, to reassume its original hose or tube diameter, in order to achieve its normal capacity.
Thus, with a larger volume of a milk charge to be delivered, its delivery takes longer, the milk sample being taken in a continuous manner and as a result of the lower speed of revolution of the peristaltic pump a higher than desired milk sample volume is taken.
Further problems in the delivery of a milk charge and taking a representative milk sample are that the delivery or pumping capacity characteristic may be influenced by factors which lead to a divergence compared with the desired or nominal delivery. Reference is e.g. made to different or too narrow cross-sections in the delivery line or in the collecting area on the milk tank. The pumping capacity can also be influenced by filter fluff in the screen of the collecting line and possibly as a result of the drive this does not coincide with the nominal capacity or delivery. The way in which the milk is collected also affects the pumping capacity, if e.g. with a relatively large air admixture, particularly at the end of the delivery operation, milk is sucked from the tank or tanks, which are subject to a downward suction action, and which can be difficult to empty due to an inadequate installation of the tank. Problems can also occur due to incorrect handling by the driver during the delivery process.
Such fault and error sources consequently influence the delivery and delivery time for transferring a milk charge from one tank into another.